The gerotor pump has emerged as a preferred means of providing lubrication for internal combustion engines attributable to its efficiency and packaging benefits. The pump is placed on center with the crankshaft axis and is generally driven by a coarse splined hub mounted on the crankshaft. The crankshaft's coarse splined hub extends through a central opening in the pump's rotor to engage female splines of the pump rotor, transferring rotational energy therebetween. Adequate clearance within the spline drive is required because tight tolerances impede assembly.
As the gerotor oil pump has become more common place in the field, unsatisfactory noise levels have been observed. Root causing the source unveiled noise introduced as a result of longitudinal crankshaft flexure during high engine loading. This longitudinal bending imparts a radial impact between the top flat of the male spline and the receiving female spline surface. Torsional shaft deflections also occur, causing tangential impacts between the radial faces of mating male and female splines. In addition, large tolerances between the mating splines generate a rattling noise from torsional spline-to-spline impacts at lower engine speeds due to pump pressure pulsations and instantaneous engine speed fluctuations. Simply increasing the clearance between the splines eliminates crankshaft motion-induced noise but aggravates drive "rattle". Resolving noise concerns will increase customer satisfaction with the engine package.